What is the Body Roundness Index?
The Body Roundness Index (BRI) was developed by mathematician Diana Thomas and colleagues in 2013. It models the body as an ellipse (an oval) using your waist circumference and height: the rounder the oval, the higher the BRI. Because it is based on your waist, BRI reflects visceral fat — the harmful fat around your organs — better than BMI, which cannot tell fat from muscle or show where fat is stored.
BRI received a lot of attention in 2024 when a large U.S. study of more than 32,000 adults (Zhang et al., JAMA Network Open) found that people with the highest BRI had a much higher risk of death over 20 years. This free BRI calculator works in centimetres or inches.
How the BRI calculator works
BRI = 364.2 − 365.5 × √(1 − [(waist ÷ 2π)² ÷ (0.5 × height)²])
Waist and height must be in the same unit. Example: a person 175 cm tall with a 90 cm waist has a BRI of about 3.6; with a 105 cm waist the BRI rises to about 5.4.
BRI chart: low, normal and high
BRI values usually range from about 1 to 16. These bands are based on the 2024 mortality study:
| BRI | Category | Level |
|---|---|---|
| Under 3.41 | Low roundness — risk slightly higher (often underweight or low muscle) | Low |
| 3.41 – 4.44 | Lean | Healthy |
| 4.45 – 5.45 | Average — lowest-risk band in the study | Healthy |
| 5.46 – 6.90 | Above average roundness | Raised |
| 6.91 and above | High roundness — about 50% higher risk of death in the study | High |
BRI vs BMI
- BMI uses weight and height only, so muscular people can look “overweight” and slim people with belly fat can look “healthy”.
- BRI uses waist and height, so it tracks belly fat and changes when your waist shrinks — even if your weight barely moves.
- BRI is newer and not yet part of most official guidelines; doctors still use BMI with waist-to-height ratio or waist size.
Benefits of checking your BRI
- Catches hidden belly fat that BMI misses.
- Motivating progress measure for waist reduction.
- Simple — just a tape measure and your height.
Health warnings
- BRI is a research tool and screening measure, not a diagnosis.
- Not valid in pregnancy, for children, or with bloating, ascites or abdominal hernias.
- Very low BRI can reflect underweight or muscle loss — check your BMI too.
- Measure in the same place each time (at the belly button) for comparable results.
How to lower your BRI
Reduce your waist with a modest calorie deficit, fewer sugary drinks and refined carbs, more fibre and protein, daily walking and strength training. Sleep and stress management matter too. See our guides on abdominal fat and sustainable weight loss.
Frequently asked questions
What is a healthy Body Roundness Index?
In a large 2024 study, a BRI between about 4.45 and 5.46 was linked with the lowest risk of death. Values from about 3.4 to 6.9 are generally considered acceptable; 6.9 or above is high.
How is BRI calculated?
BRI = 364.2 − 365.5 × √(1 − [(waist ÷ 2π)² ÷ (0.5 × height)²]), with waist and height in the same unit.
Is BRI better than BMI?
BRI reflects belly fat, which BMI cannot. Research suggests it may predict health risk better in some groups, but it is newer and not yet standard in guidelines. Using both — plus your waist measurement — gives the best picture.
What does a high BRI mean?
A high BRI means more of your body weight is around your middle, which usually means more visceral fat. This is linked to higher risk of diabetes, heart disease and early death.
How can I reduce my BRI?
Shrinking your waist reduces your BRI. Steady fat loss through diet, regular activity, strength training and good sleep is the most effective approach.
Sources
- Thomas DM, et al. Relationships between body roundness with body fat and visceral adipose tissue emerging from a new geometrical model. Obesity 2013;21:2264–2271.
- Zhang X, et al. Body roundness index and all-cause mortality among US adults. JAMA Netw Open 2024;7(6):e2415051.